But we need unions...for ...things....
What you do is levy a 100% tax on union dues. If you can afford to pay $50 a month to a do nothing union, then you can afford the same amount for healthcare, etc. No more tax-free status for unions, the union has to pay 99% of the dues received to the government. Let's so whose still pro-union when the dues rise to $5,000 a month, and they have to pay the same in taxes.